Ribosomes are macromolecular protein-RNA complexes translating mRNA into protein. To date,
crystal structures are available for the bacterial 30S and archaeal 50S subunits, as well as the
complete bacterial 70S ribosomes. Eukaryotic ribosomes are much more complex in terms of
ribosomal RNA and proteins. However, to date high-resolution crystal structures of eukaryotic
ribosomes or ribosomal subunits are lacking.
In order to build reliable models for the eukaryotic rRNA, we developed an approach for large
scale homology and de novo modeling of RNA and subsequent exible tting into high-resolution
cryo-EM density maps.
Using this approach we built a model of the T. aestivum and the S. cerevisiae ribosome based
on available cryo-EM maps at 5.5 Å and 6.1 Å resolution, respectively. The model comprises of
98% of the eukaryotic rRNA including all 21 RNA expansion segments (ES) and structurally
six variable regions. Further, we were able to localize 74/80 (92.5%) of the ribosomal proteins.
The model reveals unique ES-ES and r-protein-ES interactions, providing new insight into the
structure and evolution of the eukaryotic ribosome. Moreover, the model was used for analyzing
functional ribosomal complexes, i.e. the characterization of dierent nascent polypeptide chains
within the ribosomal tunnel, intermediates of protein translocation as well as mRNA quality
control